Titanium pigment slurries for preparation of latex-base coating compositions

ABSTRACT

An aqueous titanium dioxide slurry is prepared by adding a titanium dioxide pigment having relatively high oil absorption characteristics to water in an amount to provide a pigment concentration within the range of above 60 to no more than about 65% on a slurry weight basis, and in the presence of a dispersing agent.

United States Patent [191 Daubenspeck et al.

[ Nov. 12, 1974 TITANIUM PIGMENT SLURRIES FOR PREPARATION OF LATEX-BASE COATING COMPOSITIONS [75] Inventors: John M. Daubenspeck, Westfield;

Bernard IIolton .lett, Redbank, both of NJ.

[73] Assignee: A. L. Industries, Inc., New York,

[22] Filed: Mar. 26, 1973 [21] App]. N0.: 344,939

[52] US. Cl. 106/300, 106/308 B [51] Int. Cl. C09c 1/36 [58] Field of Search 106/300, 308 Q, 308 B [56] References Cited UNITED STATES PATENTS 3,536,510 10/1970 Allen et al. 106/300 3,702,773 1l/l972 Hall et al. l06/300 3,436,239 4/1969 Feld 106/300 3,663,284 5/1972 Starcioff et al. 106/300 3,756,841 9/1973 Beliveau 106/300 Primary Examiner-Delbert E. Gantz Assistant ExaminerJ. V. Howard [5 7 ABSTRACT 2 Claims No Drawings TITANIUM PIGMENT SLURRIES FOR PREPARATION OF LATEX-BASE COATING COMPOSITIONS BACKGROUND OF THE INVENTION The practice of shipping titanium dioxide pigment as aqueous slurry rather than as dry pigment bagged for shipment, is relatively recent and has been fostered in large measure by the increased demand for paper and latex-base coating compositions, as well as, the economic advantages attending the elimination of bagging expenses, storage sheds and handling both'by manufacture and customer. US. Pat. No. 3,663,284, May 16th, I972, discloses preparation of aqueous TiO, slurries of from 40 to 80 percent solids, as TiO wherein dispersion of the pigment is effected by adding citric or tartaric acids, or salts thereof, preferably in combination with a gum to retard settling, and a sequestering agent for calcium cations.

It has been discovered that a severe loss in tinctorial strength occurs in flat latex-base paints prepared by adding TiO pigment, having high tinctorial strength and relatively high oil absorption, as an aqueous slurry having maximum concentrations with respect to rheology, i.e., 68 to 66 percent solids. This loss in tinctorial strength may average from 150 to 300 units.

Although the exact reason for this is not known, it is postulated, on the basis of paint formulation drawdowns, that due to the highly porous nature of the hydrous oxide coatings on the pigment relatively large amounts of water are absorbed which, in conjunction with the work done on the pigment by vigorous agitation, pumping and the like, effects a certain amount of pigment agglomeration with an accompanying loss in tinting strength. Other theories suggest that the porous hydrous oxide coating is altered to reduce its effectiveness in achieving improved tinctorial strength in a given paint system.

SUMMARY OF THE INVENTION The present invention is the discovery that when preparing high solids aqueous slurries of titanium dioxide pigment for use in flat latex-base coating compositions wherein the titanium dioxide pigment is characterized by high tinctorial strength and relatively high oil absorption, that the concentration of the TiO, pigment in the aqueous slurry must be within a critical range from greater than 60 percent to no higher than 65 percent and preferably about 64 percent, on a slurry weight basis, in order to obtain latex-base coating compositions of consistantly high tinctorial strengths while accomodating latex paint formulations and minimizing slurry shipping costs.

PREFERRED EMBODIMENT OF THE INVENTION Pursuant to the objects of the present invention, aqueous slurries of titanium dioxide pigment are prepared by slurrying a titanium dioxide pigment in water in the presence of a suitable dispersing agent, the TiO, pigment being that grade of pigment commonly used in the preparation of flat latex-base paints and formulations of high pigment volume concentration. These particular titanium dioxide pigments are characterized by high tinctorial strength and relatively high oil absorption. Moreover, the aqueous slurries of this invention are prepared by adding the aforesaid'post-treated TiO, pigment to water in the presence of a suitable dispersing agent. In this connection, it has been found that a number of dispersing agents may be employed, as for example, potassium tripolyphosphate [KTPP], tetrapotassium pyrophosphate [TKPP], monoisapropanolamine [MIPA], and the like. However, from an overall standpoint, it is preferred to use KTPP in an amount from about 0.2 to about 0.7 percent, on a pigment weight basis.

The crux of the invention lies in the type and amount of posttreated TiO, pigment added to the aqueous dispersion solution. It has now been discovered that when the amount of titanium dioxide pigment added is limited to a critical range above percent to no higher than percent, on a slurry weight basis, preferably about 64 percent, latex-base paints prepared from these slurries will have uniformly high tinctorial strength. Slurries of 60 percent solids or less, as TiO, pigment, will have good tinting strength, dispersion and rheology, but will comprise so large a proportion of water as to be unsatisfactory in most paint formulations; nor would they be economical to ship.

The titanium dioxide pigment may be produced by either of the two methods commonly practiced in the industry, that is to say, by the so called sulfate process or the chloride process; and preferably in the form of rutile TiO,. Further, the pigment is characterized by relatively high oil absorption, that is to say, in the range of from above 36 to 46, as measured by the weight in gms of linseed oil required to form gms of pigment into a coherent mass. The high oil absorption is generally due to coatings of hydrous oxides, as for example, the hydrous oxides of aluminum, titanium, silicon, and mixtures thereof. Typical coatings may comprise hydrates of silica in the range of from 5 to 8% SiO alumina in the range of from 3 to 5% A1 0,, and titania in the range of from O to 2% of a TiO, weight basis.

The titanium dioxide pigment slurries of this invention were prepared by first forming an aqueous solution of a dispersion agent which in most instances was KTPP, and adding titanium dioxide pigment as rapidly as it could be wetted to the dispersion solution while agitating the latter vigorously using, for example, a dispersator fitted with a Cowles-type blade.

Pursuant to the objects of the invention, the amount of titanium dioxide pigment added was such as to provide a concentration within the range above about 60 to 65% TiO on a slurry weight basis.

TEST

The pigment may be evaluated by any latex-paint tinting strength test. The test employed for the subject examples is referred to as the Latex C Tinctorial Strength Test, and is fully described in the reference Physical Test Methods, T and D Department U S T P, issued July 5th, 1972, page P-15. Essentially, the test comprises adding the subject pigment to a composite latex vehicle containing a colorant and measuring the reflectance of the paint using a Colormaster Differential Colormeter, Model IV of V (Mfg. Eng and Equip Corp., 250 Titua Avenue, Warrington, Pa.). It is to be noted that comparisons between tinctorial strengths of paints made withdry TiO pigment vs paints made with TiO, slurries, are made at equal Ti0 pigment concentrations.

Also, all slurries were tested for dilatancy as evaluated by a Hercules High Shear viscometer operating at a maximum shear rate of 4,084 second-l.

The following examples will further serve to illustrate EXAMPLE III A third series of slurries was made using a titanium dioxide pigment post-treated with 7.5% SiO and 5% A1 The pigment had a relatively high oil absorption the invention: 0 5 of 43, and three non-dilatant slurries of different TiO EXAMPLE I I pigment concentrations were prepared as in Example The test pigment used comprised a rutile titanium di- A Shown i h t bl a l tex-base paint prepared Oxide Pigment having a Post-treatment of about 3% from a dry pigment having the same oil absorption had z and about 5% 2 3, and an Oil absorption of a tinctorial strength of 1960. The slurry having a Ti0 A series of four aqueous slurries were P p concentration of 65% produced a latex-base paint havusing the Same z p g in each instance wherein ing a tinctorial strength of 1870 while the TiO pigment slurries of various Concentrations were P p y slurries of decreasing TiO concentrations produced adding the Pigment in various amounts, to aqueous latex-base paints having steadily increasing tinctorial hltiehs Containing 07% KTPP, as the dispersing g strengths the highest being 1945 for a slurry of 60% During additions of the titanium dioxide pigment the TiQ i t tration," slurries were stirred vigorously using a dispersator equiped with a Cowles-type blade and operated at high 1 EXAMPLE v speeds. The TiO pigment slurries were then added to a standard latex-base formulation to form a paint. Data foPrth f f' F was made time using pertaining to the preparation in the testing of the four a mamum dloxlde pigment post'treined wlth, 5% S102 paint specimens are shown in the table below. 3% A1203 The plgmem had an absorption of 3 From the data, it is clear that a titanium dioxide whlch valve repfeseqts a comparatively low 9' absorp' slurry having a titanium dioxide pigment concentration valve for used m latex palm fohmw of 69% was relatively non-dilatant, its viscosity being lauons' Four flurrdes of different concentrations 25 centipoise. However, when added to a latex-base were piepared the dispersant of Example As formulation to form a paint, the tinting strength of the Show? m the t a latex'bas? palm pliepared 3 latter was only 1805 which corresponded to a decrease pllgmem g ga fii qg aborpnon a of 270 units of measure from the tinctorial strength of a d 222 3;: to i sg gg gggfz fiig latex-paint prepared from the original dry pigment. s from 65%, 64% i 60%, a" were now g F when a Slurry was prepared havmg tltamu-m dilatant and were added to latex-base formulations to roxide concentration of 65%, it was non-dilatant [vrscosity l 5 P and the latexbase paint made therefrom form latex-base paints. The latex-base paints prepared from all these slurries showed essentially equivalent had a t1nct9nal Strength 1905 slumes prepared tinctorial strengths to that of the latex paint prepared 2 gecreasmg. i p g t is i from the dry pigment. Thus, illustrating that the unexl reipectwef .orme atax' ase palms avmg pected loss in tinctorial strength that occurs when pig- Steadlly Increasing unchorial strengths Slurry. at ment slurries are used of higher than 65% TiO concen- 6 1 as Sohds pmvldmg a latexibase palm havmg tration, is confined to pigments of relatively high oil aba tinctorial strength of 2050 essentially equal to that 40 sorption Le" above of a paint prepared with dry plgment. From the foregoing description and examples, it is EXAMPLE n clear that there is a critical relationship between the pigment concentration of aqueous T10 pigment slurseries of slurries made a mamum ries used in latex-base formulations and the tinctorial dloxlde Pigment Pe with 8% and strength of the latex-base paint prepared therefrom; absorptlon was Four slurries were that pigment slurries of a concentration greater than Pared at plgrhent eeheehtratrohs of 5 63 e 65% TiO produces a serious lowering in tinctorial ,r P hf In the mariner eeserlbed above 115mg strength of a latex-base paint as compared to the tinctothe hlgh p e dlspersator for mlxmgrial strength of a latex-base paint produced by dry Ti0 AS Show" the table below, a e e Paint 0 pigment additions; that in the range of from to pared from the y Pigment e a tmetorlai Strength of above about 60% Ti0 pigment slurry concentration, 2030- Wherl Slurry of 65% 2 was used lrl P p g the tinctorial strength of the latex-base paint increases a latex-base paint, the tinctorial strength dropped to d may t ll equal th f a latexbase paint 1905; but when the TiO pigment slurries prepared at pared from a dry pigment; and, that this phenomenon Con n ra n 0f 63% n 60%, respectively, 55 is most readily apparent in titanium dioxide pigments were tested the tinctorial strengths of the latex-base characterized by high oil absorption such as usually accoating compositions prepared therefrom increased companies treatment of TiO pigment with relatively steadily to 2050 the latter being essentially that of high amounts of hydrous oxides such as silica, aluminia, the latex-base paint prepared from dry pigment. and titania.

TABLE TINCTORIAL STRENGTH PIGMENT SLURRY VISCOSITY OF LATEX-PAINT Emig- '(IQIZEATMENT CONCENggRATION AT 4084 SEC-l 0A Ti0 SLURRY Ti0 DRY I 8.0 sio, 46 2075 5.1 0 (a) 69 250p do 1805 TABLE Continued TlNCTORlAL STRENGTH PIGMENT SLURRY VISCOSITY OF LATEX-PAINT EXAM- TREATMENT CONCENTRATION AT 4084 SEC-l A Tio, SLURRY Tio, DRY

PLE ("M (h) 65 Zlcp do. I965 (c) 62 23cp do. 2010 (d) 61 22cp do. 2050 n 8.0 sio 46 2030 5.2 M 0 (:1) 65 33cp do. 1905 (b) 64 4cp do. i935 (c) 63 270p, do. 1945 (d) 60 300p do. 2050 Ill 7.5 sio 43 1960 5.0 Al o, (a) 65 206p do. 1870 (b) 64 46cp do. 1920 (c) 60 l9cp do. 1945 IV 5.0 sio 36 I890 3.0 A|,0 (a) 66 520p do. I915 (b) 65 260p do. 1895 (c) 64 2lcp do. l9l5 (d) 60 130p do. 1890 We claim: hydrous aluminum oxide and from 0 to 2 percent hydrous titanium oxide, thereby producing a coated titanium dioxide pigment having an oil absorption of from 36 to as high as 46.

2. An aqueous titanium dioxide pigment slurry according to claim 1 wherein said dispersant is potassium tripolyphosphate.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,847 .640 Dated November 12 1974 ln n fl J. M. Deubenspeck and Bernard Holton Jett It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

On face of Patent:

(73) Assignee: A L Industries, Inc., New York, N. Y.

CHANGED TO:

(73) Assignee: N L Industries Inc. New York, N. Y.

Signed and sealed this 4th day of February 1975.

(SEAL) Attest:

McCOY M. GIBSON JR. Arresting Officer C. MARSHALL DANN Commissioner of Patents FORM F'O-IOSG Ho-es) uscemwoc 60376-P69 \LS GOVEWNMENT PRINTING OFFICE: 869 9 o 

1. AN AQUEOUS TITANIUM DIOXIDE PIGMENT SLURRY HAVING A SOLIDS CONTENT FROM 60 TO 65 PERCENT ON A SLURRY WEIGHT BASIS, SAID SLURRY BEING ADAPTABLE FOR USE IN LATEX PAINTS AND COMPRISING A DISPERSING AGENT IN AN AMOUNT FROM 0.2 TO 0.7 PERCENT ON PIGMENT WEIGHT BASIS AND A TITANIUM DIOXIDE PIGMENT, SAID PIGMENT IN SAID SLURRY HAVING A POST TREATMENT COATING CONSISTING OF FROM 5 TO 8 PERCENT HYDROUS SILICON OXIDE, FROM 3 TO 5.2 PERCENT HYDROUS ALUMINUM OXIDE AND FROM 0 TO 2 PERCENT HYDROUS TITANIUM OXIDE, THEREBY PRODUCING A COATED TITANIUM DIOXIDE PIGMENT HAVING AN OIL ABSORPTION OF FROM 36 TO AS HIGH AS
 46. 2. An aqueous titanium dioxide pigment slurry according to claim 1 wherein said dispersant is potassium tripolyphosphate. 